Barcelona won a second successive league title in the 2009–10 season, securing a record 99 points. Individually, however, Iniesta endured a campaign largely disrupted by recurring injuries. He missed pre-season fitness training due to the thigh tear suffered in the 2009 Champions League final. Despite featuring in almost as many matches as the previous season, he did so mostly as a substitute, starting only 20 games throughout. His season came to a premature end in April after he aggravated a previous calf injury during training.
A contributing factor of Iniesta's fractured season were the episodes of psychological instability he suffered privately following the death of his close friend Daniel Jarque, a fellow footballer, in August 2009. Even when physically fit, he was often unable to complete training sessions or exert himself. After seeking psychological help, he experienced catharsis when he scored Spain's match-winning goal in the 2010 FIFA World Cup final, which he dedicated to Jarque by revealing the message "Dani Jarque, always with us" written on his undershirt. "I did it because I felt it deeply," Iniesta said at the time. "It showed that what is more important than rivalry, your team or your colours is to be human and a good person. I am delighted because it was the most important moment in my career." Regarding the recurrent injuries that plagued his season, he said, "It was hard, but I will start with more desire than ever."
Iniesta was selected in Spain's squad for UEFA Euro 2008 in Austria and Switzerland. Though a stomach ailment somewhat hampered his performances in the group stages, he still played an integral part in the midfield. He played in the first two of Spain's group stage matches and proved an important part of the team, providing a pass for David Villa's second goal against Russia. He was not rested, unlike most of Spain's regulars, for the final group game against Greece, which Spain won 2–1 thanks to a volley from Rubén de la Red and a late winner from Daniel Güiza. Iniesta returned for the quarter-final as Spain beat Italy on penalties; he was substituted before the penalty shootout itself. In the semi-final against Russia, he played the entire 90 minutes and produced a cross that Xavi converted to open the scoring in an eventual 3–0 victory; he was subsequently named the Man of the Match. He played the duration of the final in Spain's 1–0 win over Germany. Iniesta was named in the Team of the Tournament alongside fellow Spain midfielders Xavi, Marcos Senna and six other teammates. Iniesta did not participate in the 2009 FIFA Confederations Cup in South Africa due to a thigh muscle injury; Spain was eliminated from the tournament at the semi-final stage.